In general, an embroidery machine is a two-axes positioning control machine in that an embroidery frame anchoring a piece of cloth horizontally moves in X- and Y-directions while a needle bar for executing a sewing operation moves vertically.
A needle bar vertical drive unit for vertically driving the needle bar is installed within the sewing arm of the embroidery machine, and an upper shaft providing force for driving the needle bar vertical drive unit is installed through the sewing arm, wherein the noise and vibration are produced most within the sewing arm when the needle bar is driven. Reducing the noise and vibration within is the most important factor in increasing the work speed of the machine.
FIG. 1 is a schematic perspective view showing a sewing arm mechanism of a conventional embroidery machine, and FIG. 2 is an exploded perspective view of the sewing arm mechanism shown in FIG. 1. A needle bar vertical drive unit for vertically driving a needle bar (not shown) with the rotational driving force of an upper shaft 2 is installed within the sewing arm 1 of the embroidery machine, and the upper shaft 2 is installed through the sewing arm 1, wherein a needle bar drive cam 4 is fitted on the periphery of the upper shaft 2.
In addition, a needle bar drive rod 3 is installed on the periphery of the needle bar drive cam 4, and the upper shaft 2 is provided with a thread take-up lever bar drive cam base 5, and a thread take-up lever drive cam 6, beyond the needle bar drive cam 4, wherein the thread take-up lever drive cam base 5 and the thread take-up lever drive cam 6 sequentially cooperate with the needle bar drive cam 4.
Because the reaction force produced due to the rotation of the needle bar drive cam 4 installed on the upper shaft 2 and formed in an eccentric configuration, and the reaction force produced due to the driving of the needle bar vertical drive unit act on the upper shaft, the needle bar vertical drive unit installed within the sewing arm 1 as described above produces vibration and noise within the sewing arm 1 when the upper shaft 2 rotates.
FIG. 3 is an upper shaft diagram showing reaction force acting on an upper shaft diagram in a conventional embroidery machine. Here, the upper shaft 2 is configured in such a manner that the reaction force, which is exerted on the upper shaft 2 as the needle bar drive cam 4 is rotated when the upper shaft 2 rotates, and the reaction force, which is exerted on the upper shaft 2 as the needle bar vertical drive unit is driven, simultaneously act on the upper shaft 2. As a result, when the rotating velocity of the upper shaft 2 is increased, substantially high load acts on the upper shaft 2, thereby producing a lot of vibration and noise within the sewing arm 1 as well as fracturing or deforming the upper shaft 2.
If vibration and noise are produced within the sewing arm 1 as mentioned above, it is difficult to increase the rotating speed of the upper shaft 2 over a predetermined level. In addition, the vibration and noise afford the upper shaft 2 high impulsive load, thereby greatly vibrating various components of the machine as well as the upper shaft 2. As a result, the endurance of the components is deteriorated.